No my Scarlett Johanssen moment that did it for me was the opening shot in
Lost in Translation She didn’t have to say a word her, laying there looking out the window at the city skyline of Tokoyo was enough for me.
Bingo.
For Jean-Paul Belmondo, it is his scene where, shirtless, a cigarette dangling from his mouth, he tries to convince Jean Seberg to sleep with him again, in Godard’s Breathless.
When Lauren Bacall gave instructions on how to whistle.
Ewan McGregor laughing at the driver of the car that just hit him in Trainspotting.
I think it’s when she walked down the hallway between the two other girls in Jawbreaker.
Although he’d been in a number of moderately popular films before this, I’d have to say that Michael Keaton’s defining moment came when he had the bad guy by the collar, looked into his eyes and said, in a calm but menacing tone, “Tell them … I’m Batman.”
Robin Williams shouting “Gooooooood morning, Vietnam!” into the mic. (Although “I vant to defect” in Moscow on the Hudson could be a contender. I’m not counting his time as Mork, though)
I could be imagining all this but the scene in my head involved two palm trees pulling apart his legs via rope during a training montage.
It’s been a while since I’ve seen this movie.
oh and here’s another one.
Bruce Willis inside the ventilation duct with a zippo lighter held in front of his face talking about how great it’ll be to go to LA and celebrate Christmas.
John Travolta dancing in:
(a)Saturday Night Fever
(b)Grease
©Pulp Fiction
(d)All of the above
Johnny Depp looking over his shoulder and grinning, showing his gold teeth, as he and Orlando Bloom are stealing the Dauntless. He was a star before, but that shot made him a superstar.
Mark Hamill taking off the stormtrooper mask and saying “I’m Luke Skywalker. I’m here to rescue you.”
Richard E. Grant:
I DEMAND to have some BOOZE!!!
Nope, Keaton’s was long before that, in Night Shift: “Is this a great country, or what?”
Rupert Everett snarking away with Julia Roberts in My Best Friend’s Wedding. Test screening audiences liked his character so much they filmed additional footage of him, IIRC.
Sophia Loren had starred in Italian movies for a number of years, but I believe it was her appearance in “Boy On A Dolpin” that really endeared her to American audiences.
I think this “visual aid” might help convince most folks that this was the shot that made her a star. 
Oh my, yes! When that movie first came out, there was a review in my local newspaper with this headline:
The Two Reasons for Sophia Loren’s Stardom!
(Don’t know how that slipped past the censors.)
Later it turned out that Sophia wasn’t just a life-support system for boobs, but could really act. But her initial impact on audiences wasn’t related to acting talent.
Strother Martin in those mirrored sunglasses.
You’re not thinking about Cool Hand Luke are you? If so, that wasn’t Strother.
My mistake, haven’t seen that movie in a long time.
Okay. Strother is the one with the “communicate” line. The Boss with the glasses and the rifle is Morgan Woodward not to be confused with Morgan Freeman. 
